1. Field of the Invention
The present invention relates to a printer apparatus for printing an image on a recording medium by discharging a discharging medium filled in a pressure chamber from a discharge nozzle by a bimorphic effect of a piezoelectric element and a vibrating plate and to a method of production of the same.
2. Description of the Related Art
The conventional so-called "on-demand type" ink jet printer is a printer which discharges ink droplets from a nozzle in accordance with a recording signal so as to record an image on a recording medium such as paper or film. This printer enables a reduction of size and a reduction of cost, so has been rapidly spreading in recent years.
On the other hand, in recent years, particularly in the office, there has been a boom in the production of documents by computers in what is known as "desk top publishing". Recently, there has been increased demand for printing not only characters and figures, but also color natural images such as photographs together with the characters and figures. To print a high quality natural image in this way, reproduction of halftones is very important.
In this on-demand type ink jet printer, the general methods used to discharge the ink droplets have been the method of using for example a piezoelectric element and the method of using a heat generating element. The method of using a piezoelectric element uses the deformation of the piezoelectric element to give a pressure to the ink and thereby discharge the same from the nozzle. On the other hand, the method of using the pressure of bubbles generated by heating and boiling the ink by a heat generating element to discharge the ink.
To reproduce halftones, there are the method of changing the voltage given to the piezoelectric element or the heat generating element and the pulse width so as to control the size of the droplets to be discharged, thereby making variable the diameter of the printing dots and expressing a tone and the method of including a pixel by a matrix consisting of for example 4.times.4 dots without a change of the dot diameter and expressing the tones by using the so-called dither method in units of this matrix.
The method of using the deformation of a piezoelectric element to give pressure to the ink and discharge the same from a nozzle includes a method in which a plurality of superposed layers of piezoelectric elements are made to linearly displaced to push the vibrating plate and a method of giving a voltage to a piezoelectric element including a single layer or two superposed layers clad to a vibrating plate so as to cause the vibrating plate to bend.
FIG. 1 and FIG. 2 show a print head in a printer apparatus using a single-plate type piezoelectric element. This print head comprises a base 101 made of for example a photosensitive glass, a vibrating plate 102 attached to this base 101, a piezoelectric element 103 provided on this vibrating plate 102, and an orifice plate 105 on which the discharge nozzle 104 is formed.
On the base 101, as shown in FIG. 1, an ink introduction hole 106 for introducing the ink and a pressure chamber 107 for accommodating the ink are formed. The vibrating plate 102 is attached to the base 101 so as to cover these ink introduction hole 106 and pressure chamber 107. The piezoelectric element 103 has electrodes 108 and 109 on the upper and lower surfaces of its thickness direction as shown in FIG. 1, respectively, and is bonded onto the vibrating plate 102 at a position corresponding to the pressure chamber 107 by an adhesive or the like. The orifice plate 105 is provided on the surface of the base 101 opposite to the surface on which the vibrating plate 102 is provided. The discharge nozzle 104 provided on this orifice plate 105 is communicated with the pressure chamber 107.
In this print head, when a voltage is applied to the piezoelectric element 103, the piezoelectric element 103 deforms due to the bimorphic effect and the displacement thereof is transferred to the pressure chamber 107 via the vibrating plate 102. Then, due to the displacement of this piezoelectric element 103, the volume of the pressure chamber 107 is reduced and the ink filled in the pressure chamber 107 is discharged from the discharge nozzle 104.
In the method of bending the vibrating plate by giving a voltage to a piezoelectric element including a single layer or two superposed layers adhered to the vibrating plate, however, there is a problem that it is difficult to achieve a fine pitch when adhering cut piezoelectric elements onto a vibrating plate. Further, where arranging paste-like piezoelectric elements on the vibrating plate by a means such as printing and then performing sintering, the heat resistance of the vibrating plate makes it difficult to raise the sintering temperature to 1000.degree. C. or more, so there is the defect that the characteristic of the piezoelectric material cannot be sufficiently exhibited. Further, in the method of cutting after adhering a piezoelectric element to a vibrating plate, it is difficult to cut only the piezoelectric element without scratching the vibrating plate and, at the same time, it is not easy to always cut to a constant depth when considering the wear of the tool and the positional precision of the machine tool.
On the other hand, in the method of causing straight displacement of a plurality of layers of superposed piezoelectric elements to push the vibrating plate, the piezoelectric elements per se become expensive so there is a disadvantage in view of costs.